1. Field of the Invention
The present invention relates to a sealing composition. More particularly, it relates to a sealing composition comprising low melting devitrifiable glass powder and low thermal expansion crystalline powder which achieves a seal at the devitrified state by a heat-treatment at a relatively lower temperature and which is suitable for sealing a panel (face plate) and a funnel of a color television tube.
2. Description of the Prior Arts
Heretofore, it has been known to use PbO--B.sub.2 O.sub.3 --ZnO--SiO.sub.2 type low melting devitrifiable glass solder disclosed in British Pat. No. 863,500, for sealing a panel and a funnel of a color television tube.
When the conventional glass solder is used, in order to achieve a satisfactory seal, it has been necessary to provide a heat-treatment at 440.degree. to 450.degree. C. for about 1 hour.
The heat-treatment at high temperature may cause a transformation of the sealed parts such as the panel and funnel and it may cause a thermal transformation of the other parts heated at high temperature during the heat-treatment, such as a shadow mask whereby it has been required to lower the temperature in the sealing step. It is also required to lower the sealing temperatare to save the energy.